Deoxygenated blood returns to the heart, where it enters the right atrium through the <span>superior and inferior vena cava. It then goes to the right ventricle through the tricuspid valve, after which it is pumped to the pulmonary artery through the pulmonary valve. The pulmonary valve splits in two and is connected to the lungs, where the blood is pushed through capillaries in the lungs and is oxygenated and drops CO2. It then goes into the pulmonary vein and goes into the left atrium of the heart, after which it enters the left atrium, then goes through the mitral valve to the left ventricle, where it is pumped into the aorta through the aortic valve and distributed throughout the body, becoming deoxygenated and completing the cycle.</span>
Carbohydrates do not have a carbon nitrogen-bond because nitrogen is not found in this protein. So the answer is C) carbohydrate. I hope this helps.
I think it’s C explanation : i learned this a while ago
